The present invention relates to a pattern formation method employed in semiconductor fabrication process.
In accordance with the increased degree of integration of semiconductor integrated circuits and the downsizing of semiconductor devices, development of lithography technique is desired to be accelerated.
At present, patterns are formed through photolithography using a mercury lamp, KrF excimer laser or ArF excimer laser as exposing light. In order to form a fine pattern of 0.1 xcexcm or less and particularly 50 nm or less, application of exposure in vacuum with extreme UV (i.e., light of a wavelength of a 1 nm through 30 nm band) or electron beams to the exposing light is now under examination. Also, as a resist material suitable to such exposing light, a chemically amplified resist material with high resolution and sensitivity is used.
Now, a conventional pattern formation method in which pattern exposure is performed by irradiating a resist film made of a chemically amplified resist material with extreme UV in vacuum will be described with reference to FIGS. 4A through 4D.
First, a chemically amplified resist material having the following composition is prepared:
Next, as shown in FIG. 4A, the chemically amplified resist material is applied on a semiconductor substrate 1 by spin coating, so as to form a resist film 2 with a thickness of 0.2 xcexcm. Thereafter, the resist film 2 is subjected to baking 3 for pre-bake at a temperature of 90xc2x0 C. for 60 seconds with a hot plate.
Then, as shown in FIG. 4B, pattern exposure is performed by irradiating the pre-baked resist film 2 with extreme UV 4 of a wavelength of 13.5 nm in vacuum through a reflection mask not shown.
Thereafter, as shown in FIG. 4C, the resist film 2 is subjected to baking 5 at a temperature of 110xc2x0 C. for 60 seconds with a hot plate. Thus, an exposed portion 2a of the resist film 2 becomes soluble in an alkaline developer owing to a function of an acid generated from the acid generator while an unexposed portion 2b of the resist film 2 remains insoluble in an alkaline developer because no acid is generated therein.
Subsequently, as shown in FIG. 4D, the resist film 2 is developed with a 2.38 wt % tetramethylammonium hydroxide developer (alkaline developer), so as to form a resist pattern 6 with a line width of 0.07 xcexcm.
As shown in FIG. 4D, however, the resultant resist pattern 6 is degraded in its cross-sectional shape.
The degradation in the shape of the resist pattern 6 seems to be caused for the following reason:
In the pattern exposure performed by irradiating the pre-baked resist film 2 with extreme UV 4 in vacuum, an outgas is generated from the resist film 2 and the generated outgas adheres onto a mirror or a mask of an exposure optical system. Therefore, the illuminance of the exposing light used for irradiating the resist film 2 is lowered, and hence, a sufficient amount of acid cannot be generated from the acid generator in the exposed portion 2a of the resist film 2.
In consideration of the aforementioned conventional problem, an object of the invention is forming a resist pattern in a good cross-sectional shape by reducing the amount of outgas generated from a resist film during pattern exposure.
In order to achieve the object, the pattern formation method of this invention includes the steps of performing pre-bake on a resist film; vaporizing a solvent included in the resist film after the pre-bake; performing pattern exposure by selectively irradiating the resist film with exposing light in vacuum after vaporizing the solvent; and forming a resist pattern by developing the resist film after the pattern exposure.
In the pattern formation method of this invention, after vaporizing the solvent included in the pre-baked resist film, the resist film is subjected to the pattern exposure in vacuum. Therefore, the amount of outgas generated from the resist film during the pattern exposure is largely reduced, and the amount of acid generator and the like leaked to the outside with the solvent in vacuum is reduced. Accordingly, the amount of outgas adhered onto a mirror or a mask of an exposure optical system can be remarkably reduced, and the illuminance of the exposing light irradiating the resist film can be increased. As the result, a resist pattern can be formed in a good cross-sectional shape.
In the pattern formation method of this invention, in the step of vaporizing a solvent, an amount of solvent included in the resist film after vaporizing the solvent is preferably reduced to 10% or less of an amount of solvent included in the resist film before the pre-bake.
Thus, the amount of outgas generated from the resist film during the pattern exposure can be definitely reduced.
In the pattern formation method of this invention, the step of vaporizing a solvent preferably includes a sub-step of baking the resist film after the pre-bake.
Thus, the solvent included in the resist film can be easily and definitely vaporized.
In the pattern formation method of this invention, the step of vaporizing a solvent preferably includes a sub-step of irradiating the resist film with an energy beam after the pre-bake.
Thus, the solvent included in the resist film can be easily and definitely vaporized.
In this case, the energy beam is preferably UV or deep UV.
Thus, the solvent included in the resist film can be vaporized without inducing the resist film with the energy beam.
In the pattern formation method of this invention, the resist film is preferably made of a chemically amplified resist material.
In this case, a base polymer of the chemically amplified resist material may be a phenol polymer, an acrylic polymer, a methacrylic polymer or a cycloolefin polymer.
In the pattern formation method of this invention, the exposing light can be extreme UV of a wavelength of a 1 nm through 30 nm band or an electron beam.
Alternatively, in the pattern formation method of this invention, the exposing light can be extreme UV of a wavelength of a 13.5 nm band.